Lens assemblies used with today""s cameras generally incorporate both an automatic focus function and a zoom function. The zoom function is provided by a zoom lens that is generally controlled by a direct current (DC) motor that changes the relationship among the lens components to enable magnification of the image. The focus function is provided by a focus lens, which is generally actuated by a stepper motor that controls the relative positioning of lens assembly components to bring the subject into focus at an image plane. The two functions of focus and zoom are related in that if the zoom changes, the focus also generally changes in a proportional manner.
Generally, the focus steps provided by the stepper motor are related to the focus distance over which the lens is designed to operate. For example, in a macro photograph implementation, the lens may have a focus range of, for example, 100 to 1000 millimeters (mm). This focus range generally corresponds to a number of steps through which the focus motor causes the lens to move to achieve focus. For example, a focus range of 100-1000 mm may equate to focus steps of 20-40, with 0 being what is referred to as the xe2x80x9chomexe2x80x9d position of the lens.
In a typical implementation, the zoom function is actuated by a user of the camera to generally frame the subject of the image to be captured. Once the zoom function is completed, the focus function is activated by, for example, by partially pressing a shutter-actuating button on the camera.
A common focus mode is to move the focus lens into a fixed position where objects that are far away, referred to as at an xe2x80x9cinfinitexe2x80x9d distance, are in focus. This mode allows users to capture an image of a distant subject without going through a focus process. The exact position of the focus motor for this mode can be calibrated at the lime the camera is manufactured.
Other calibrations are also performed when the camera is manufactured. For example, a relationship between a focus search range (i.e., the number of steps to scan a focus mechanism) to ensure proper focus of the lens over a focus range (i.e., 100-1000 mm as described above) is generally set during the manufacturing process. However, during operation, the camera is subject to operational temperatures that may vary significantly from the temperature at which the camera and its focus mechanism were calibrated. As the temperature of the camera and the lens changes, the relationship among the components that comprise the lens changes as well. Consequently, if a focus mechanism relies solely on calibrated relationships to focus the lens, operational temperatures that vary from the temperature of the lens during calibration will cause the calibrated position to be inaccurate. As a result, captured images will be out of focus.
To account for temperature related focus errors, camera designers generally apply a liberal search range through which the focus motor adjusts components of the lens to ensure that a subject-of-interest at a given focus range can be properly focused. Accordingly, this results in the need to expand the range of steps through which the lens motor must step to achieve acceptable focus for a given focus range. Unfortunately, expanding the range of steps through which the focus motor must adjust the lens increases the time it takes to achieve an acceptably focused image of the subject-of-interest, thereby increasing the amount of time required to capture an image. This delay in achieving a focused image is bothersome to a user of the camera.
Therefore, it is desirable to reduce the amount of time consumed in achieving focus with a lens coupled to a camera and in positioning a lens so that distant subjects are in focus without additional adjustment.
Systems and methods for estimating lens temperature in a camera are invented and disclosed. In one embodiment, a method for estimating the temperature of a camera lens, comprises the steps of sensing temperature at a location within the body of a camera, monitoring the occurrence and duration of or/off operating states of heat generating elements of the camera, and using the temperature at a location within the body of the camera and monitored occurrence and duration of on/off operating states of heat generating elements within the camera body to determine a current temperature of a lens assembly coupled to the camera.